Cold Room

[kothari]

:confused: What can be the reason to have high Relative Humidity(RH 80%)in my cold storage even though the temperature is maintained about 38 Ferenheat

[paulcollis]

Depending on product in your room i would say 80% Rh isnt overly high, but depending on design parameters and size of evaporator coil, will greatly effect split across the coil, eg the greater the split the lower the humidity, the lesser the split the more humidity, for example if you have a room at 3 degrees celcius and your evaporating temp 0 dgrees then your split is a lot less than say a normal 6k split were you would evaporate at -5 to 6 dgrees, the higher the split the more free moisture is removed from the air and condensates on the coil therefore going down the drain. Cheers Paul

[wambat]

The dew point at those conditions is 32.5*f so your air off temp must be below this temperature.

[US Iceman]

High humidity can be required by the product being stored. For example, if the cooler stores fresh produce that has a high water content (like lettuce) you want high humidity to keep the product from drying out.

A lower volume of air circulation also helps, since the higher air circulation increases the transfer of moisture from the product to the evaporator coil.

If the coil temperature (evaporating temp.) is a lot lower than the room temperature, more moisture is transffered to the coil at a faster rate. This is the higher coil split, or greater temperature difference (room temperature minus coil temperature), and lower room humidity.

The opposite is true for lower temperature differences (lower coil split).

If the product is shrink wrapped in plastic, the plastic acts as a vapor barrier. The vapor barrier prevents the moisture from leaving the product (packaged cut meat for example).

In this case, the product is protected and can withstand higher air velocities and higher splits, without drying out the product.

Any moisture that leaves the product also reduces the weight of the product. Since most perishable products are sold by weight, the water loss affects the sellers profit. The product can also taste or appear different, which also affects sales.

The water loss from the product is called "shrinkage".

Hope this helps you,
US Iceman

[Peter_1]

:confused: What can be the reason to have high Relative Humidity(RH 80%)in my cold storage even though the temperature is maintained about 38 Ferenheat

What's stored in this room?
What are the compressor its working conditions?
What are the room conditions?

[kothari]

What's stored in this room?
What are the compressor its working conditions?
What are the room conditions?
Ans.
It is a wrapped food products.the moisture can not escape from theproducts.
The compressor works on the remote place having evoparator coils (spit in three) in the coldroom
Room well enclosed isulated.

[Peter_1]

Well, if the food is wrapped, what is then teh evaporating temperature and room temperature?
You're perhaps evaporating too high.

Brand and type of both evaporators and compressor?
Size of room?
Refrigeration system oversized and compressors doesn't run long enough to remove moisture in the air.

Record humidity for a complete day, preferable with a logger.

Then, if you have 3 evaporators, shutt off one of the 2 with the SV or if it's only one SV for the 3 evaporators, turn in completely the TEV of 2 evaporators for some days to see what happens on the humidity. Make sure temeprature remains within your specs.

Another test which can pinpoint the problem: install after your first humidity readings some electrical heaters in the room and see what happens with the RH.

Post then your findings aftwerwards here on this forum so that we can help further.
It's up to you to perform the same tests over there we otherwise should do to find the problem.

[chilly]

Is there by any chance a gap around the door seal? are there any holes or any way air can be escaping or penatrating the cold room? Is the door opened alot, is the cold room situated in a humid kitchen?

[dill]

you say you have 3 evaps in the room, could they by chance have individual defrost times or too longer defrosts creating high humidities that way?

[botrous]

The relative humidity in cold stores usually depends on the difference between the coolant tempreture and the refrigeration room tempreture, here you will find an attached diagram on how relative humidity changes with the tempreture difference (the diagram is extracted from "General manual of refrigeration" publisher ElettronicaVeneta Italy) , hope it will be useful to give you an idea . . . as delta T increases the relative humidity decreases , take a look at the attachement .

Best regards